Fluoroolefin/vinyl alcohol copolymer and process for its production

ABSTRACT

To provide a process for producing a fluoroolefin/vinyl alcohol copolymer with sufficiently high productivity and excellent heat resistance, whereby a quality loss by coloration is prevented, and a fluoroolefin/vinyl alcohol copolymer obtainable by such a process. A process for producing a fluoroolefin/vinyl alcohol copolymer, which comprises a polymerization step of copolymerizing a specific fluoroolefin and a vinyl ether having a hydrogen atom of a hydroxy group of a vinyl alcohol substituted with a protective group which can be deprotected, and a deprotection step of substituting the protective group in polymerized units based on the vinyl ether in the copolymer obtained in the polymerization step, with a hydrogen atom to form a hydroxyl group, and the fluoroolefin/vinyl alcohol copolymer obtainable by such a process.

TECHNICAL FIELD

The present invention relates to a fluoroolefin/vinyl alcohol copolymerand a process for its production.

BACKGROUND ART

A fluoroolefin/vinyl alcohol copolymer, i.e. a copolymer of afluoroolefin and vinyl alcohol, is used as a raw material for coatingresins, a material for gas/liquid separation membranes, a gas barriermaterial, a sealing material for solar cells, a material for varioussurface protective sheets, a hydrophilic porous material, etc. (Patentdocuments 1 and 2).

As a method for producing a fluoroolefin/vinyl alcohol copolymer, amethod has already been known wherein a fluoroolefin and vinyl acetateare copolymerized, followed by hydrolysis under an acidic or basiccondition (Patent Documents 1 and 2, and Non-Patent Document 3). In sucha method, a fluoroolefin and vinyl acetate are used as raw materials,and they are copolymerized to obtain a fluoroolefin/vinyl acetatecopolymer, and in such a copolymer, an ester moiety in polymerized unitsbased on vinyl acetate is hydrolyzed to form a hydroxy group thereby toconvert the polymerized units to ones based on vinyl alcohol. However,in the method of hydrolyzing the fluoroolefin/vinyl acetate copolymerunder a basic condition, although the reaction rate is high, theobtainable copolymer is likely to be colored yellow, whereby the productquality tends to be low. Whereas, in the method of hydrolyzing thefluoroolefin/vinyl acetate copolymer under an acidic condition, thereaction rate is low, and the productivity is low. Further, the obtainedfluoroolefin/vinyl alcohol copolymer usually has a low thermaldecomposition starting temperature and thus has a problem in thermalstability.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-A-5-261256-   Patent Document 2: JP-A-6-1876

Non-Patent Document

-   Non-Patent Document 1: M. Ragazzini et. al., Eur. Polym. J., 3, 5    (1967)

DISCLOSURE OF INVENTION Technical Problem

It is an object of the present invention to provide a process forproducing a fluoroolefin/vinyl alcohol copolymer which has sufficientlyhigh productivity and heat resistance, whereby a quality loss bycoloration is prevented, and a fluoroolefin/vinyl alcohol copolymerobtainable by such a process.

Solution to Problem

In order to solve the above problem, the present invention provides aprocess for producing a fluoroolefin/vinyl alcohol copolymer, and afluoroolefin/vinyl alcohol copolymer, having the followingconstructions.

[1] A process for producing a fluoroolefin/vinyl alcohol copolymer,which comprises a polymerization step of copolymerizing a fluoroolefinrepresented by the following formula (1) and a vinyl ether representedby the following formula (2), and a deprotection step of substituting R¹in polymerized units based on the vinyl ether in the copolymer obtainedin the polymerization step, with a hydrogen atom to form a hydroxygroup:

CF₂═CFX  (1)

CH₂═CHOR¹  (2)

wherein X is a fluorine atom, a chlorine atom, a trifluoromethyl groupor —OC_(a)F_(2a+1) (wherein a is an integer of from 1 to 3), and R¹ is aprotective group to be substituted with a hydrogen atom by adeprotection reaction.

[2] The process for producing a fluoroolefin/vinyl alcohol copolymeraccording to the above [1], wherein R¹ in the formula (2) is —CR²R³R⁴(wherein each of R², R³ and R⁴ which are independent of one another, isa C₁₋₃ alkyl group), a C₁₋₆ alkoxymethyl group, a tetrahydrofuryl group,a tetrahydropyranyl group or a trialkylsilyl group (—Si(R⁵)₃ wherein R⁵is a C₁₋₆ alkyl group or an aryl group).

[3] The process for producing a fluoroolefin/vinyl alcohol copolymeraccording to the above [1], wherein the compound represented by theformula (2) is t-butyl vinyl ether.

[4] The process for producing a fluoroolefin/vinyl alcohol copolymeraccording to any one of the above [1] to [3], wherein R¹ is substitutedwith a hydrogen atom by an acid.

[5] The process for producing a fluoroolefin/vinyl alcohol copolymeraccording to any one of the above [1] to [4], wherein in thepolymerization step, the molar ratio of the fluoroolefin represented bythe formula (1) to the vinyl ether represented by the formula (2) i.e.(fluoroolefin)/(vinyl ether) is from 45/55 to 55/45.

[6] The process for producing a fluoroolefin/vinyl alcohol copolymeraccording to any one of the above [1] to [5], wherein a vinyl etherrepresented by the following formula (3) is further copolymerized:

CH₂═CHOR⁶  (3)

wherein R⁶ is a group which is not susceptible to a deprotectionreaction in the deprotection step.

[7] A fluoroolefin/vinyl alcohol copolymer having an alternatingcopolymerization rate of a fluoroolefin represented by the followingformula (1) and vinyl alcohol being at least 95%:

CF₂═CFX  (1)

wherein X is a fluorine atom, a chlorine atom, a trifluoromethyl groupor —OC_(a)F_(2a+1) (wherein a is an integer of from 1 to 3).

[8] The fluoroolefin/vinyl alcohol copolymer according to the above [7],which has a 10 mass % thermal decomposition starting temperature of atleast 340° C.

Advantageous Effects of Invention

According to the process of the present invention, it is possible toproduce a fluoroolefin/vinyl alcohol copolymer excellent in heatresistance with sufficiently high productivity, whereby a quality lossdue to coloration is prevented.

Further, the fluoroolefin/vinyl alcohol copolymer of the presentinvention has a quality loss due to coloration prevented and hasexcellent heat resistance.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(A) and (B) are ¹³C NMR charts of copolymer B1 (upper chart) andcopolymer A1 (lower chart) in Example 1.

FIGS. 2(A) and (B) are IR charts of copolymer B1 and copolymer A1 inExample 1, respectively.

DESCRIPTION OF EMBODIMENTS

The process for producing a fluoroolefin/vinyl alcohol copolymer of thepresent invention (hereinafter referred to as “the copolymer (A)”)comprises the following steps.

Polymerization step: a step of copolymerizing a fluoroolefin representedby the following formula (1) (hereinafter referred to as “thefluoroolefin (a)”) and a vinyl ether represented by the followingformula (2) (hereinafter referred to as “the vinyl ether (b)”).

Deprotection step: a step of substituting R¹ in polymerized units basedon the vinyl ether (b) in the copolymer obtained in the polymerizationstep, with a hydrogen atom to form a hydroxy group.

CF₂═CFX  (1)

CH₂═CHOR¹  (2)

wherein X is a fluorine atom, a chlorine atom, a trifluoromethyl groupor —OC_(a)F_(2a+1) (wherein a is an integer of from 1 to 3), and R¹ is aprotective group to be substituted with a hydrogen atom by adeprotection reaction.

That is, the process of the present invention is a process wherein inthe polymerization step, a fluoroolefin/vinyl ether copolymer(hereinafter referred to as “the copolymer (B)”) having polymerizedunits based on the fluoroolefin (a) and polymerized units based on thevinyl ether (b) is obtained, and then, R¹ in polymerized units based onthe vinyl ether (b) in the copolymer (B) is substituted with a hydrogenatom by a deprotection reaction, to obtain the copolymer (A) havingpolymerized units based on the fluoroolefin and polymerized units basedon vinyl alcohol.

Polymerization Step:

In the polymerization step, the fluoroolefin (a) represented by theabove formula (1) and the vinyl ether (b) represented by the aboveformula (2) are copolymerized to obtain the copolymer (B) havingpolymerized units based on the fluoroolefin (a) and polymerized unitsbased on the vinyl ether (b).

A specific example of the fluoroolefin (a) may, for example, betetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene or aperfluoro(alkyl vinyl ether). The perfluoro(alkyl vinyl ether) may, forexample, be perfluoro(propyl vinyl ether). Among them, the fluoroolefin(a) is preferably tetrafluoroethylene or chlorotrifluoroethylene,particularly preferably tetrafluoroethylene, whereby the heat resistancewill be excellent.

As the fluoroolefin (a), one type may be used alone, or two or moretypes may be used in combination.

The vinyl ether (b) is a vinyl ether having a hydrogen atom of a hydroxygroup of vinyl alcohol substituted with a protective group which can bedeprotected.

R¹ is a protective group which protects a hydroxy group in the form ofan ether and which is substituted with a hydrogen atom by a deprotectionreaction to form a hydroxy group, and a protective group which iscommonly used in the organic chemical field may be used. From theviewpoint of availability, —CR²R³R⁴ (wherein each of R², R³ and R⁴ whichare independent of one another, is a C₁₋₃ alkyl group), a C₁₋₆alkoxymethyl group, a tetrahydrofuryl group, a tetrahydropyranyl groupor a trialkylsilyl group (—Si(R⁵)₃ wherein R⁵ is a C₁₋₆ alkyl group oran aryl group) is preferred, and —CR²R³R⁴ is more preferred.

As the vinyl ether (b), t-butyl vinyl ether, 1,1-dimethylpropyl vinylether, methoxymethyl vinyl ether, tetrahydrofuryl vinyl ether,tetrahydropyranyl vinyl ether, vinyloxytrimethylsilane orvinyloxydimethylphenylsilane is preferred, and from the viewpoint ofavailability, t-butyl vinyl ether is particularly preferred.

As the vinyl ether (b), one type may be used alone, or two or more typesmay be used in combination.

The fluoroolefin (a) and the vinyl ether (b) have high alternatingcopolymerizability, and therefore, the alternating copolymerization rateof the obtainable copolymer (B) becomes at least 95% as calculated byprobability calculation from the copolymerization reactivity ratio ofthe two monomers. The alternating copolymerization rate is thepercentage of the number of combinations where polymerized units basedon different monomers are adjacent to each other, based on the totalnumber of combinations of adjacent two polymerized units. For example,in a case where the copolymer (B) is a copolymer represented byababbababab (wherein a is a polymerized unit based on the fluoroolefin(a), and b is a polymerized unit based on the vinyl ether (b)), thetotal number of combinations of adjacent two polymerized units is 10,and the number of combinations where polymerized units based ondifferent monomers are adjacent to each other, is 9, and therefore, thealternating copolymerization rate is 90%.

Since the alternating copolymerization rate of the copolymer (B) is atleast 95%, the copolymer (A) obtainable from the copolymer (B) will havean alternating copolymerization rate of the fluoroolefin (a) and vinylalcohol being at least 95%. In the copolymer (A) having such a highalternating copolymerization rate, polymerized units based on thefluoroolefin (a) and polymerized units based on vinyl alcohol areuniformly arranged, whereby the weather resistance and water resistanceare improved. Further, for example, in a case where a curing agent is tobe reacted to hydroxy groups in the copolymer (A) to form a curedproduct, the reactivity of hydroxy groups is more stabilized, since thehydroxy groups are uniformly distributed.

In the polymerization step to obtain the copolymer (B), in addition tothe fluoroolefin (a) and the vinyl ether (b), a vinyl ether (c)represented by the following formula (3) may further be copolymerized.

CH₂═CHOR⁶  (3)

wherein R⁶ is a group which is not susceptible to a deprotectionreaction in the deprotection step.

The vinyl ether (c) is a vinyl ether wherein R⁶ is not susceptible to adeprotection reaction in the deprotection step. “R⁶ is not susceptibleto a deprotection reaction in the deprotection step” means that R⁶ isnot susceptible to a deprotection reaction under the reaction conditionswhere R¹ in the vinyl ether (b) is substituted with a hydrogen atom bythe deprotection reaction. That is, R⁶ may be a group which issusceptible to a deprotection reaction under conditions other than thereaction conditions where R¹ is substituted with a hydrogen atom by thedeprotection reaction.

When the vinyl ether (c) is used, R⁶ in polymerized units based on thevinyl ether (c) in the copolymer (B) will not be deprotected in thedeprotection step, and the polymerized units based on the vinyl ether(c) will be maintained as they are, in the obtainable copolymer (A).

R⁶ in the vinyl ether (c) is preferably a C₁₋₆ primary or secondaryalkyl group, or a group having at least one of hydrogen atoms in such analkyl group substituted by a substituent. The substituent may, forexample, be a functional group such as a hydroxy group, an amino groupor a glycidyl group, a fluorine atom, or the like.

A specific example of the vinyl ether (c) may, for example, be an alkylvinyl ether such as methyl vinyl ether, ethyl vinyl ether, n-butyl vinylether, isobutyl vinyl ether or cyclohexyl vinyl ether; a functionalgroup-containing vinyl ether such as hydroxyethyl vinyl ether,hydroxybutyl vinyl ether, aminopropyl vinyl ether or glycidyl vinylether; or a fluorinated vinyl ether such as heptafluoropentyl vinylether.

In a case where the vinyl ether (c) is used, a vinyl ether of either oneof the vinyl ether (b) and the vinyl ether (c), and the fluoroolefin (a)are alternately copolymerized to obtain the copolymer (B). The vinylether (b) and the vinyl ether (c) are substantially equal in thepolymerization reactivity, and therefore, it is a question ofprobability that both sides of a polymerized unit based on thefluoroolefin (a) in the copolymer (B) become either a polymerized unitbased on the vinyl ether (b) or a polymerized unit based on the vinylether (c).

In a case where the vinyl ether (c) is used, no deprotection reactiontakes place at polymerized units based on the vinyl ether (c) in thecopolymer (B). Therefore, by adjusting the ratio of the vinyl ether (b)to the vinyl ether (c), it is possible to adjust the proportion ofpolymerized units based on vinyl alcohol in the copolymer (A) after thedeprotection step. Thus, by adjusting the amount of hydroxy groups inthe copolymer (A), it is possible to adjust the hydrophilicity of thecopolymer (A).

By subjecting the fluoroolefin (a), the vinyl ether (b) and, as the caserequires, the vinyl ether (c) to radical polymerization, the copolymer(B) is obtainable. A monomer having a vinyl ether group (the vinyl ether(b) or the vinyl ether (c)) is likely to undergo isomerization,decomposition or cationic homopolymerization under an acidic condition.Therefore, with a view to carrying out the polymerization stably, it ispreferred to carry out the radical polymerization under a basiccondition, and it is more preferred to adjust the pH to be from 8 to 9.As a method of adjusting the pH to be under a basic condition in thepolymerization, a method of adding e.g. potassium carbonate or ammoniumcarbonate to the polymerization medium, is preferred.

In a case where no vinyl ether (c) is used, the molar ratio (a/b) of thefluoroolefin (a) to the vinyl ether (b) to be used for thecopolymerization, is preferably from 40/60 to 60/40, more preferablyfrom 45/55 to 55/45, particularly preferably 50/50. When the molar ratio(a/b) is within the above range, it is possible to readily obtain analternate copolymer having the fluoroolefin (a) and the vinyl ether (b)alternately copolymerized.

Further, in a case where the vinyl ether (c) is used, the molar ratio(a/(b+c)) of the fluoroolefin (a) to the total of the vinyl ether (b)and the vinyl ether (c) to be used for the copolymerization, ispreferably from 40/60 to 60/40, more preferably from 45/55 to 55/45,particularly preferably 50/50. When the molar ratio (a/(b+c)) is withinthe above range, it is possible to readily obtain an alternate copolymerhaving the fluoroolefin (a) and the vinyl ether (b) or the vinyl ether(c) alternately copolymerized.

Further, in such a case, the molar ratio (b/c) of the vinyl ether (b) tothe vinyl ether (c) is preferably 45/5 to 10/40, particularly preferablyfrom 40/10 to 25/25.

As the radical polymerization initiation source, a radicalpolymerization initiator or an ionizing radiation may be mentioned. Asthe radical polymerization initiator, a water-soluble initiator or anoil-soluble initiator may suitably be used depending upon thepolymerization type or the polymerization medium.

The water-soluble initiator may, for example, be a redox initiatorcomposed of a combination of a persulfate such as ammonium persulfate,and a reducing agent such as hydrogen peroxide, sodium hydrogen sulfiteor sodium thiosulfate; an inorganic initiator having a small amount ofiron, a ferrous salt or silver nitrate incorporated to the above redoxinitiator; or an organic initiator, such as a dibasic acid peroxide suchas disuccinic acid peroxide or diglutaric acid peroxide, or a dibasicacid salt such as azobisisobutylamidine.

The oil-soluble initiator may, for example be a peroxyester typeperoxide such as t-butyl peroxyacetate or t-butyl peroxypivalate; adialkylperoxydicarbonate such as diisopropylperoxydicarbonate; benzoylperoxide; or azobisisobutylnitrile.

As the radical polymerization initiator, t-butyl peroxypivalate may, forexample, be preferred, from the viewpoint of handling efficiency, etc.

As the radical polymerization initiator, one type may be used alone, ortwo or more types may be used in combination.

The amount of the radical polymerization initiator may be suitablychanged depending upon the type, polymerization conditions, etc., and itis preferably from 0.005 to 5 mass %, particularly preferably from 0.05to 0.5 mass %, based on the total amount of monomers to be used for thecopolymerization.

The copolymerization type is not particularly limited, and bulkpolymerization, suspension polymerization, emulsion polymerization orsolution polymerization may, for example, be employed. Among them,solution polymerization is preferred wherein an aromatic compound suchas xylene or toluene, an alcohol such as t-butyl alcohol, an ester, afluorochlorocarbon or the like is used as the polymerization medium.

The amount of the polymerization medium is preferably from 10 to 200mass %, particularly preferably from 50 to 100 mass %, based on thetotal amount of monomers to be used for the copolymerization.

Further, the copolymerization system may be any one of a batch system, acontinuous system and a semicontinuous system.

With respect to the copolymerization temperature, the optimum value maysuitably be selected depending upon the polymerization initiationsource, the polymerization medium, etc., and it is preferably from −30°C. to 150° C., more preferably from 0° C. to 100° C., most preferablyfrom 20° C. to 70° C.

Likewise, the polymerization pressure may suitably be selected dependingupon the polymerization initiation source, the polymerization medium,etc., and it is preferably from 0.1 to 10 MPa, particularly preferablyfrom 0.2 to 2 MPa.

The copolymerization time is preferably from 4 to 24 hours, morepreferably from 6 to 12 hours.

The molecular weight of the copolymer (B) may be adjusted by controllingthe ratio of the monomers and the polymerization medium or by employinga chain transfer agent.

The number average molecular weight (Mn) of the copolymer (B) ispreferably from 3,000 to 300,000, more preferably from 10,000 to300,000. When Mn of the copolymer (B) is at least 3,000, the toughnessof a coating film may easily be maintained. When Mn of the copolymer (B)is at most 300,000, formation of a film or sheet becomes easy.

Further, in a case where the application is in the coating field, Mn ofthe copolymer (B) is preferably from 3,000 to 30,000. In a case where itis used as a film or sheet, Mn of the copolymer (B) is more preferablyfrom 10,000 to 100,000.

The molecular weight distribution (Mw/Mn) of the copolymer (B) ispreferably from 1 to 3, more preferably from 1 to 2. When Mw/Mn of thecopolymer (B) is at most 3, an improvement in the coating productivityor an improvement in the film strength can be expected.

Deprotection Step:

In the deprotection step, R¹ in polymerized units based on the vinylether (b) in the copolymer (B) obtained in the above polymerizationstep, is substituted with a hydrogen atom by a deprotection reaction toform a hydroxy group, whereby the polymerized units based on the vinylether (b) are converted to polymerized units based on vinyl alcohol, toobtain the copolymer (A) having polymerized units based on thefluoroolefin (a) and polymerized units based on vinyl alcohol. In a casewhere polymerized units based on the vinyl ether (c) are contained inthe copolymer (B), R⁶ in polymerized units based on the vinyl ether (c)is maintained as it is without undergoing a deprotection reaction,whereby the copolymer (A) having polymerized units based on thefluoroolefin (a), polymerized units based on vinyl alcohol andpolymerized units based on the vinyl ether (c), will be obtained.

As a method for substituting R¹ in polymerized units based on the vinylether (b) in the copolymer (B) with a hydrogen atom by the deprotectionreaction, a deprotection reaction of a protected alcohol by an acid,heat or light, which is commonly carried out, may be employed. Amongthem, it is preferred to substitute R¹ with a hydrogen atom by an acid,since it is thereby easy to prevent coloration of the obtainablecopolymer (A).

The acid to be used for the deprotection reaction may, for example, bean inorganic acid such as sulfuric acid, hydrochloric acid or nitricacid, or an organic acid such as acetic acid, butyric acid ortrifluoroacetic acid.

The deprotection reaction by an acid is preferably (1) a deprotectionreaction in a mixed solution of sulfuric acid/ethanol/water, (2) adeprotection reaction in a mixed solution of hydrochloric acid/dioxaneor (3) a deprotection reaction in a mixed solution of trifluoroaceticacid/methylene chloride. However, the deprotection reaction by an acidis not particularly limited to the reaction system of the above (1) to(3) and may be carried out in an aqueous system or in a non-aqueoussystem.

Further, the deprotection reaction by an acid may be carried out byusing a photo-acid-generator which generates an acid under irradiationwith light. Such a photo-acid-generator may, for example, be an oniumsalt, a halogenated compound, a diazoketone compound, a sulfone compoundor a sulfonic acid compound. A specific example may, for example, bediphenyl iodonium triflate, triphenyl sulfonium triflate,phenyl-bis(trichlorimethyl)-s-triazine,methoxyphenyl-bis(trichloromethyl)-s-triazine, 4-trisphenancyl sulfoneor 1,8-naphthalenedicarboxylic acid imide triflate.

In the deprotection step, depending upon a particular application of thecopolymer (A), the deprotection reaction may be terminated halfwaybefore all of protective groups in the copolymer (B) are deprotected, toobtain the copolymer (A) having polymerized units based on thefluoroolefin (a), polymerized units based on the vinyl ether (b) andpolymerized units based on vinyl alcohol. By adjusting the ratio ofpolymerized units based on the vinyl ether (b) to polymerized unitsbased on vinyl alcohol by terminating the deprotection reaction halfway,it is possible to adjust the hydrophilicity, crystallinity, etc. of theobtainable copolymer (A).

By the above-described process of the present invention, in thedeprotection at the polymerized units based on vinyl ether (b) of thecopolymer (B), coloration is prevented as is different from aconventional method for hydrolyzing a fluoroolefin/vinyl acetatecopolymer obtained by copolymerizing a fluoroolefin and vinyl acetate.Further, even in the case of the deprotection by an acid, a sufficientreaction rate can be obtained. Therefore, it is possible to produce ahigh quality fluoroolefin/vinyl alcohol copolymer with sufficiently highproductivity. In the present invention, a factor whereby thedeprotection by an acid proceeds at a sufficient reaction rate, isconsidered to be such that the etheric oxygen atom of the vinyl ether(b) is likely to more readily undergo protonation than the acetic acidgroup of vinyl acetate.

Further, in the conventional copolymerization of a fluoroolefin andvinyl acetate, the fluoroolefin and vinyl acetate are randomlycopolymerized, whereby the alternating copolymerizability of the twomonomers is low. And, the positions of hydroxy groups in thefluoroolefin/vinyl alcohol copolymer obtainable from such afluoroolefin/vinyl acetate copolymer, are also random. Therefore, insuch a fluoroolefin/vinyl alcohol copolymer, the properties arenon-uniform as between portions where the proportion of polymerizedunits based on the fluoroolefin is high and portions where theproportion of polymerized units based on vinyl alcohol is high, andaccordingly, the water resistance and heat resistance tend to be low.

Whereas, according to the process of the present invention, thefluoroolefin (a) and the vinyl ether (b) or vinyl ether (c) aresubstantially alternately polymerized, whereby hydroxy groups will beuniformly distributed in the polymer chain. Therefore, hydroxy groupsare not concentrated at specific sites, and it is possible to preventthat hydrophilicity of specific portions of the polymer chain becomesextremely high, and the copolymer (A) will exhibit excellent waterresistance. Further, in the copolymer (A), polymerized units based onvinyl alcohol are not concentrated at specific sites, whereby excellentheat resistance can readily be obtainable.

The heat resistance of the copolymer (A) can be evaluated by thelater-described 10 mass % thermal decomposition starting temperature(hereinafter referred to also as “Td¹⁰[° C.]”). The 10 mass % thermaldecomposition starting temperature of the copolymer (A) obtainable bythe present invention is preferably at least 340° C., more preferablyfrom 360 to 400° C.

For example, in a case where the copolymer (A) is used as a coatingmaterial, it is possible to form a coating film having hydroxy groupsuniformly arranged. Further, from a composition comprising the copolymer(A) and a curing agent such as melamine or isocyanate reactive withhydroxy groups, it is possible to form a film or coating film made of acured product having a crosslinked structure. In such a case, it is alsopossible to obtain such an effect that by uniformly distributing hydroxygroups without using the vinyl ether (c), the reactivity of hydroxygroups can be constantly obtained. Further, in a case where a curingagent is employed as mentioned above, timing for carrying out thedeprotection step is not particularly limited, and for example, acomposition obtained by mixing the copolymer (B), a component such as anacid to be used for the deprotection reaction and a curing agent, etc.is formed into a film or sheet and then light or heat is applied to formhydroxy groups to obtain a film or sheet made of a cured product havinga crosslinked structure. That is, in such a case, the vinyl ethermoieties in the copolymer (B) may be used as potential curing moieties.

EXAMPLES

Now, the present invention will be described in detail with reference toExamples and Comparative Examples. However, it should be understood thatthe present invention is by no means restricted by the followingdescription.

[Measuring Methods] (Number Average Molecular Weight (Mn), MolecularWeight Distribution (Mw/Mn))

The number average molecular weight (Mn) and the molecular weightdistribution (Mw/Mn) of a copolymer obtained in each Example weremeasured by gel permeation chromatography (GPC) using a high speed GPCapparatus “HLC-8220GPC” manufactured by Tosoh Corporation. Their valuesare calculated values using polystyrene as standard substance. As theeluent, tetrahydrofuran was used.

(Glass Transition Temperature)

The glass transition temperature of a copolymer was measured by using“DSC Q-100” manufactured by TA Instruments Japan Inc., in a N₂ gasatmosphere at a temperature raising rate of 10° C./min.

(10 Mass % Thermal Decomposition Starting Temperature)

The 10 mass % thermal decomposition starting temperature of a copolymerwas measured by using TGA Q-500 manufactured by TA Instruments JapanInc., in air at a temperature raising rate of 10° C./min.

(Copolymer Composition)

The copolymer composition of a copolymer was calculated from thefluorine mass analytical values of the copolymer. However, in Example 6,the calculation was made by further combining the results of ¹³C-NMRmeasurement.

(Structure of Copolymer)

The structure of a copolymer was identified from the measurements of theIR spectrum, ¹H-NMR and ¹³C-NMR spectra.

Example 1

Polymerization Step:

Into a stainless steel autoclave having an internal capacity of 200 mLand equipped with a stirrer (pressure resistance: 3 MPa), 79.0 g oft-butyl alcohol, 26.7 g of t-butyl vinyl ether (hereinafter referred toas “TBVE”) as the vinyl ether (b), 0.48 g of potassium carbonate and0.46 g of an isooctane solution containing 70% of perbutyl perpivarate(hereinafter referred to as “PBPV”) were charged, and the oxygen in thesystem was removed by repeating pressure purging with N₂ gas. Then, 26.7g of tetrafluoroethylene (hereinafter referred to as “TFE”) as thefluoroolefin (a) was introduced into the autoclave, followed by heatingto 55° C. The pressure at that time was 1.56 MPa. Then, polymerizationwas continued for 7 hours, and when the pressure decreased to 1.12 MPa,the autoclave was cooled with water, and non-reacted TFE was purged toterminate the polymerization. The obtained polymer solution was put intomethanol to precipitate the formed copolymer B1, followed by vacuumdrying. The yield of the copolymer B1 was 22.0 g, and the conversion ofthe monomers was 41%. The ¹³C-NMR spectrum of the copolymer B1 is shownin FIG. 1(A), and the IR spectrum is shown in FIG. 2(A).

As a result of the fluorine mass analysis, the copolymer compositionalratio of the copolymer B1 was TFE/TBVE=51/49 (mol %). Further, by acalculation from the copolymerization reactivity ratio of both monomers,it was found to have a substantially alternating structure (alternatingcopolymerization rate: at least 95%).

Deprotection Step:

2.0 g of the copolymer B1, 0.5 mL of concentrated sulfuric acid, 50 mLof ethanol and 1 mL of water were put into a 100 mL flask, heated andstirred at 90° C. to carry out a deprotection reaction. This reactionsystem became a uniform solution in from 3 to 4 hours. The reaction wascontinued for a total of 12 hours, and then, the reaction solution wasdropped into water to precipitate a copolymer, which was washed withwater and then vacuum-dried at 40° C. to isolate 1.42 g of whitecopolymer A1. The ¹³C-NMR spectrum of the copolymer A1 is shown in FIG.1(B), and the IR spectrum is shown in FIG. 2(B).

By the measurements of the ¹³C-NMR spectrum and the IR spectrum, it wasconfirmed that in the copolymer A1, at least 97% of protective groups(t-butyl groups) were eliminated by hydrolysis to form hydroxy groups.

Example 2

The copolymer B1 obtained in Example 1 was used.

Deprotection Step:

2.0 g of the copolymer B1, 50 mL of 4N hydrochloric acid and 1 mL of1,4-dioxane were put into a 100 mL flask, heated and stirred at 90° C.to carry out a deprotection reaction. This reaction system graduallybecame a uniform solution. The reaction was continued for a total of 12hours, and then, the reaction solution was dropped into water toprecipitate copolymer A2, which was washed with water and thenvacuum-dried at 40° C. to isolate 1.49 g of the copolymer A2.

By the measurements of the ¹H-NMR spectrum and the IR spectrum, it wasconfirmed that in the copolymer A2, at least 97% of protective groups(t-butyl groups) were eliminated.

Example 3

The copolymer B1 obtained in Example 1 was used.

Deprotection Step:

2.0 g of the copolymer B1, 50 mL of trifluoroacetic acid and 1 mL ofmethylene chloride were put into a 100 mL flask and then stirred at roomtemperature. The reaction was continued for a total of 48 hours, andthen, the precipitated copolymer was washed with water and thenvacuum-dried at 40° C. to isolate 1.33 g of the copolymer A3.

By the measurements of the ¹H-NMR spectrum and the IR spectrum, it wasconfirmed that in the copolymer A3, at least 97% of protective groups(t-butyl groups) were detached.

Example 4

Polymerization Step:

Into a stainless steel autoclave having an internal capacity of 30 mLand equipped with a stirrer (pressure resistance: 3 MPa), 8.97 g oft-butyl alcohol, 7.74 g of tetrahydropyranyl vinyl ether (hereinafterreferred to as “THPVE”) as the vinyl ether (b), 0.124 g of potassiumcarbonate and 0.298 g of an isooctane solution containing 70% of PBPVwere charged, and the oxygen in the system was removed by repeatingpressure purging with N₂ gas. Then, 6.1 g of TFE was introduced into theautoclave, followed by heating to 65° C. The pressure at that time was1.75 MPa. Then, polymerization was continued for 5 hours, and when thepressure decreased to 0.59 MPa, the autoclave was cooled with water, andnon-reacted TFE was purged to terminate the polymerization. The obtainedpolymer solution was put into methanol to precipitate the formedcopolymer B2. The yield of the copolymer B2 was 9.04 g, and theconversion of the monomers was 65.3%.

As a result of the fluorine mass analysis, the copolymer compositionalratio of the copolymer B2 was TFE/TBVE=47/53 (mol %). By a calculationfrom the copolymerization reactivity ratio of both monomers, it wasfound to have a substantially alternating structure (alternatingcopolymerization rate: at least 95%).

Deprotection Step:

The deprotection step was carried out in the same manner as in Example 1except that the copolymer B2 was used, to obtain copolymer A4.

By the measurements of the ¹³C-NMR spectrum and the IR spectrum, it wasconfirmed that in the copolymer A4, at least 95% of protective groups(tetrahydropyranyl groups) were eliminated.

Example 5

Polymerization Step:

Into a stainless steel autoclave having an internal capacity of 200 mLand equipped with a stirrer (pressure resistance: 3 MPa), 79.0 g oft-butyl alcohol, 26.7 g of TBVE, 0.52 g of potassium carbonate and 0.47g of an isooctane solution containing 70% of PBPV were charged, and theoxygen in the system was removed by repeating pressure purging with N₂gas. Then, 31.1 g of chlorotrifluoroethylene (hereinafter referred to as“CTFE”) as the fluoroolefin (a) was introduced into the autoclave,followed by heating to 55° C., and polymerization was continued for 7hours. Then, the autoclave was cooled with water, and non-reacted CTFEwas purged to terminate the polymerization. The obtained polymersolution was put into methanol to precipitate the formed copolymer B3.The yield of the copolymer B3 was 10.22 g, and the conversion of themonomers was 17.7%.

As a result of the fluorine mass analysis, the copolymer compositionalratio of the copolymer B3 was CTFE/TBVE=49/51 (mol %).

Deprotection Step:

The deprotection step was carried out in the same manner as in Example 1except that the copolymer B3 was used, to obtain copolymer A5.

By the measurements of the ¹³C-NMR spectrum and the IR spectrum, it wasconfirmed that in the copolymer A5, at least 95% of protective groups(t-butyl groups) were eliminated. The glass transition temperature ofthe copolymer A5 was not clear.

Example 6

Polymerization Step:

Into a stainless steel autoclave having an internal capacity of 200 mLand equipped with a stirrer (pressure resistance: 3 MPa), 79.0 g oft-butyl alcohol, 13.4 g of TBVE, 16.8 g of cyclohexyl vinyl ether(hereinafter referred to as “CHVE”) as the vinyl ether (c), 0.52 g ofpotassium carbonate and 0.51 g of an isooctane solution containing 70%of PBPV were charged, and the oxygen in the system was removed byrepeating pressure purging with N₂ gas. Then, 26.7 g of CTFE wasintroduced into the autoclave, followed by heating to 55° C., andpolymerization was continued for 7 hours. Then, the autoclave was cooledwith water, and non-reacted CTFE was purged to terminate thepolymerization. The obtained polymer solution was put into methanol toprecipitate the formed copolymer B4, followed by vacuum drying. Theyield of the copolymer B4 was 30.1 g, and the conversion of the monomerswas 53%.

As a result of the fluorine mass analysis and the ¹³C-NMR measurement,the copolymer compositional ratio of the copolymer B4 wasCTFE/TBVE/CHVE=51/24/25 (mol %). Further, by a calculation from thecopolymerization reactivity ratio of the monomers, it was found to havea substantially alternating structure (alternating copolymerizationrate: at least 95%).

Deprotection Step:

The deprotection step was carried out in the same manner as in Example 1except that the copolymer B4 was used, to obtain copolymer A6.

By the measurements of the ¹H-NMR spectrum and the IR spectrum, it wasconfirmed that in the copolymer A6, at least 95% of protective groups(t-butyl groups) were eliminated. Further, from the fluorine massanalysis, the polymerized units based on CHVE were confirmed to haveremained as they were.

Comparative Example 1

Polymerization Step:

Into a stainless steel autoclave having an internal capacity of 200 mLand equipped with a stirrer (pressure resistance: 3 MPa), 61.9 g ofmethyl acetate, 9.1 g of vinyl acetate (hereinafter referred to as“VAc”) and 0.39 g of an isooctane solution containing 70% of PBPV werecharged, and the oxygen in the system was removed by repeating pressurepurging with N₂ gas. Then, 20.9 g of TFE was introduced into theautoclave, followed by heating to 55° C. The pressure at that time was1.23 MPa. Then, polymerization was continued for one hour, and when thepressure decreased to 0.75 MPa, the autoclave was cooled with water, andnon-reacted TFE was purged to terminate the polymerization. The obtainedpolymer solution was put into methanol to precipitate copolymer C1,followed by vacuum drying. The yield of the copolymer C1 was 18.5 g, andthe conversion of the monomers was 62%.

As a result of the fluorine mass analysis, the copolymer compositionalratio of the copolymer C1 was TFENAc=49/51 (mol %). The alternatingcopolymerization rate of the copolymer C1 was from 80 to 85% by acalculation from the copolymerization reactivity ratio of both monomers.

Deprotection Step:

2.0 g of the copolymer C1, 0.5 mL of concentrated sulfuric acid, 50 mLof ethanol and 1 mL of water were put into a 100 mL flask, and whileheating and stirring at 90° C., a reaction was carried out for 24 hours.After the reaction, the deprotection rate was calculated from thefluorine mass analytical value and found to be about 50%. When theheating was further continued, the reaction system gradually became auniform solution. The reaction was continued for a total of 72 hours,and then, the reaction solution was dropped into water to precipitatecopolymer D1, which was washed with water and then vacuum-dried at 40°C. to isolate 1.42 g of the copolymer D1.

By the measurements of the ¹³C-NMR spectrum and the IR spectrum, it wasconfirmed that in the copolymer D1, at least 97% of protective groups(acetyl groups) were eliminated to form hydroxy groups.

Comparative Example 2

The copolymer C1 obtained in Comparative Example 1 was used.

Deprotection Step:

2.0 g of the copolymer C1, 50 mL of ethanol and 3.5 mL of a 30 mass %sodium hydroxide aqueous solution were put into a 100 mL flask, andwhile heating and stirring at 90° C., a reaction was carried out for 24hours, whereby the reaction system became reddish brown. The reactionsolution was dropped into water to precipitate copolymer D2, which waswashed water and then vacuum-dried at 40° C. to isolate 1.46 g of thecopolymer D2. The copolymer D2 was colored yellow.

Comparative Example 3

Polymerization Step:

Into a stainless steel autoclave having an internal capacity of 200 mLand equipped with a stirrer (pressure resistance: 3 MPa), 79.0 g oft-butyl alcohol, 33.6 g of CHVE, 0.54 g of potassium carbonate and 0.46g of an isooctane solution containing 70% of PBPV were charged, and theoxygen in the system was removed by repeating pressure purging with N₂gas. Then, 26.7 g of TFE was introduced into the autoclave, followed byheating to 55° C. The pressure at that time was 1.54 MPa. Then,polymerization was continued for 6 hours, and when the pressuredecreased to 0.75 MPa, the autoclave was cooled with water, andnon-reacted TFE was purged to terminate the polymerization. The obtainedpolymer solution was put into methanol to precipitate copolymer C2,followed by vacuum drying. The yield of the copolymer C2 was 42.2 g, andthe conversion of the monomers was 70%.

As a result of the fluorine mass analysis, the copolymer compositionalratio of the obtained copolymer C2 was TFE/CHVE=50/50 (mol %).

Deprotection Step:

The deprotection reaction was attempted under the same conditions as inExample 1 by using the copolymer C2. After heating and stirring for 48hours, copolymer D3 was recovered and vacuum dried. The copolymer D3 wasanalyzed by the IR spectrum, whereby it was found that there was nochange in the spectrum as between before and after the reaction, and thedeprotection reaction did not proceed. That is, the copolymer D3 was thesame copolymer as the copolymer C2.

With respect to the copolymers obtained in Examples and ComparativeExamples, the results of measurements of the number average molecularweight (Mn), the molecular weight distribution (Mw/Mn), the glasstransition temperature (Tg), the 10 mass % thermal decompositionstarting temperature (Td₁₀) and the melting point (Tm), and presence orabsence of coloration after the deprotection step, are shown in Table 1.

TABLE 1 Polymerization step Deprotection step Tg Td10 Tg Td10 TmMonomers Mn Mw/Mn [° C.] [° C.] Mn Mw/Mn [° C.] [° C.] [° C.] ColorationEx. 1 TFE/TBVE 21600 1.67 34 341 19100 1.77 75-80 366 207 Nil Ex. 2TFE/TBVE 21600 1.67 34 341 20900 1.74 75-80 376 206 Nil Ex. 3 TFE/TBVE21600 1.67 34 341 19500 1.91 75-80 365 206 Nil Ex. 4 TFE/THPVE 376002.88 39 389 28200 2.95 75-80 389 207 Nil Ex. 5 CTFE/TBVE 13500 2.02 63263 11600 2.23 Not 310 168 Nil known Ex. 6 CTFE/TBVE/CHVE 18800 2.15 38351 17700 2.29  35 340 Nil Nil Comp. TFE/VAc 38000 2.79 40 341 321002.90 65-70 322 212 Nil Ex. 1 Comp. TFE/VAc 38000 2.79 40 341 30500 2.95320 320 212 Observed Ex. 2 Comp. TFE/CHVE 16800 1.98 43 360 The reactiondid not proceed. Ex. 3

As shown in Table 1, the copolymers (A1 to A4) in Examples 1 to 4produced by using the vinyl ether (b) had no coloration and had a highquality. Further, the copolymers (A1 to A6) obtained in Examples 1 to 6had high 10 mass % thermal decomposition starting temperatures and wereexcellent in heat resistance.

Whereas, the copolymers (D1 and D2) in Comparative Example 1 and 2produced by using vinyl acetate, had lower 10 mass % thermaldecomposition starting temperatures as compared with the copolymers (A1to A4) in Examples 1 to 4 and were inferior in heat resistance. This isconsidered to be such that since polymerized units based on vinylacetate were consecutively arrayed, portions where polymerized unitsbased on vinyl alcohol were consecutively arrayed, were formed, and suchportions were likely to be broken by heat.

Further, the deprotection step by an acid in Comparative Example 1required 72 hours and thus was inferior in the productivity as comparedwith 12 hours as required in the deprotection step by an acid under thesame conditions in Example 1.

Further, the copolymer D2 in Comparative Example 2 produced byhydrolyzing the copolymer C1 produced by using vinyl acetate, under abasic condition, was inferior in quality with coloration to yellowobserved.

Further, in Comparative Example 3 (Copolymer C2) wherein only the vinylether (c) was used without using the vinyl ether (b) in the deprotectionstep, the deprotection reaction did not proceed, and the desiredcopolymer (A) was not obtained.

INDUSTRIAL APPLICABILITY

The copolymer (A) obtainable by the process of the present invention isuseful as e.g. a raw material for coating material excellent in weatherresistance and transparency, an optical material excellent intransparency, a gas/liquid separation film material excellent in waterresistance, a gas barrier material, a sealing material for solar cells,a material for various surface protective sheets, a hydrophilic porousmaterial, etc.

This application is a continuation of PCT Application No.PCT/JP2011/058736, filed Apr. 6, 2011, which is based upon and claimsthe benefit of priority from Japanese Patent Application No. 2010-089504filed on Apr. 8, 2010. The contents of those applications areincorporated herein by reference in its entirety.

1. A process for producing a fluoroolefin/vinyl alcohol copolymer, whichcomprises a polymerization step of copolymerizing a fluoroolefinrepresented by the following formula (1) and a vinyl ether representedby the following formula (2), and a deprotection step of substituting R¹in polymerized units based on the vinyl ether in the copolymer obtainedin the polymerization step, with a hydrogen atom to form a hydroxygroup:CF₂═CFX  (1)CH₂═CHOR¹  (2) wherein X is a fluorine atom, a chlorine atom, atrifluoromethyl group or —OC_(a)F_(2a+1) (wherein a is an integer offrom 1 to 3), and R¹ is a protective group to be substituted with ahydrogen atom by a deprotection reaction.
 2. The process for producing afluoroolefin/vinyl alcohol copolymer according to claim 1, wherein R¹ inthe formula (2) is —CR²R³R⁴ (wherein each of R², R³ and R⁴ which areindependent of one another, is a C₁₋₃ alkyl group), a C₁₋₆ alkoxymethylgroup, a tetrahydrofuryl group, a tetrahydropyranyl group or atrialkylsilyl group (—Si(R⁵)₃ wherein R⁵ is a C₁₋₆ alkyl group or anaryl group).
 3. The process for producing a fluoroolefin/vinyl alcoholcopolymer according to claim 1, wherein the compound represented by theformula (2) is t-butyl vinyl ether.
 4. The process for producing afluoroolefin/vinyl alcohol copolymer according to claim 1, wherein R¹ issubstituted with a hydrogen atom by an acid.
 5. The process forproducing a fluoroolefin/vinyl alcohol copolymer according to claim 1,wherein in the polymerization step, the molar ratio of the fluoroolefinrepresented by the formula (1) to the vinyl ether represented by theformula (2) i.e. (fluoroolefin)/(vinyl ether) is from 45/55 to 55/45. 6.The process for producing a fluoroolefin/vinyl alcohol copolymeraccording to claim 1, wherein a vinyl ether represented by the followingformula (3) is further copolymerized:CH₂═CHOR⁶  (3) wherein R⁶ is a group which is not susceptible to adeprotection reaction in the deprotection step.
 7. A fluoroolefin/vinylalcohol copolymer having an alternating copolymerization rate of afluoroolefin represented by the following formula (1) and vinyl alcoholbeing at least 95%:CF₂═CFX  (1) wherein X is a fluorine atom, a chlorine atom, atrifluoromethyl group or —OC_(a)F_(2a+1) (wherein a is an integer offrom 1 to 3).
 8. The fluoroolefin/vinyl alcohol copolymer according toclaim 7, which has a 10 mass % thermal decomposition startingtemperature of at least 340° C.